The present invention relates to the bead portion of a pneumatic tire, and more specifically of a tire for heavy duty use, comprising a bead core with a round or polygonal shape, an apex, a carcass comprising three reinforcing structures, comprising each at least one reinforcing ply.
Radial carcass tires for heavy duty use are often used under heavy load conditions which place the components within a tire under severe stress. The bead regions of such tires are particularly subject to large deformations caused by flexing of the sidewalls which can produce sheer stresses between the carcass plies and heat build-up.
The desirability of having the turn-up portions of the carcass ply (or plies) of a pneumatic tire extend radially outwardly of the bead core the shortest possible distance is the premise on which prior art locked beads for passenger car tires were developed. The advantages included improved bead durability, and reduced material costs.
U.S. Pat. No. 4,922,985 discloses a passenger car tire with a carcass ply having a main portion that extends between both beads of the tire and turn-up portions that are anchored around each bead core. Tires according to this prior art and according to U.S. Pat. 5,058,649 have the radially outer edges of the turn-up portions of the carcass ply disposed radially outwardly of the bead cores a minimal distance and are in contact with the main portion of the carcass ply. The turn-up portion of the carcass ply extends radially outwardly of the bead core a minimal distance to allow for some pull-down of the carcass ply during the shaping and curing process.
Components that are usually located in the bead portion of tires include a toe guard and a chafer strip. A toe guard is a layer of reinforcing cords folded around the carcass ply and bead core on the side of the carcass ply furthest away from the bead core. The primary purpose of a toe guard is to protect the bead from damage during mounting of the tire on a rim and subsequent use of the tire on a vehicle. A chafer may be either a tough elastomeric material that protects the bead portion from abrasion during mounting and use of the tire, or a layer of fabric extending from the bead core to about the same radial height as the edge of the turn-up. Suitable elastomeric materials surround the bead core and coat the carcass plies and the breaker plies; other elastomeric components complete the bead portion of the tire.
It is an object of the present invention to provide a tire construction with particularly durable bead portions which are cheap to manufacture. It is a further object of the present invention to improve the locking of at least one of the carcass plies in the bead portion. Other objects of the invention will be apparent from the following description and claims.
There is provided, in accordance with the invention, a pneumatic tire having (a) a pair of axially spaced apart bead portions with annular bead cores, each bead core having a radial cross-sectional shape which is substantially round or polygonal; and (b) a pair of rubber apex strips of a generally triangular cross-section neighboring the bead cores the apex stripes having a radial height A and extending radially outwardly from the bead cores into the sidewalls of the tire; and (c) at least three sets, a first radially inner, a second intermediate and a third radially outer set of carcass reinforcing structures, having each a main portion extending between the beads and their edges anchored in the beads. The second carcass reinforcing structure is folded radially outwardly around each said bead core, so that the two edges of the second carcass reinforcing structure are located between the apexes and their neighboring bead cores. The third carcass reinforcing structure has its turndown portions folded radially inwardly around the second carcass reinforcing structure and the bead cores, so that the edges of the plies of the third carcass reinforcing structure are located at the radially inner side of the bead cores. The first carcass reinforcing structure has its turnup portions folded radially outwardly around each bead core, the second carcass reinforcing structure and the third carcass reinforcing structure so that the edges of the plies of the first carcass reinforcing structure are located between the radially outer portion of the bead core and the maximum section height of the tire.
There is further provided a pneumatic tire having (a) a pair of axially spaced apart bead portions with annular bead cores, each bead core having a radial cross-sectional shape which is substantially round or polygonal; (b) a pair of rubber apex strips of a generally triangular cross-section neighboring the bead cores, the apex strips having a radial height A and extending radially outwardly from the bead cores into the sidewalls of the tire, (c) a first bead wrap ply structure; (d) at least two sets, a second intermediate and a third radially outer set of carcass reinforcing structures, having each a main portion extending between the beads and their edges anchored in the beads. The second carcass reinforcing structure is folded radially outwardly around each said bead core, so that the two edges of the second carcass reinforcing structure are located between the apexes and their neighboring bead cores. The third carcass reinforcing structure has its turndown portions folded radially inwardly around the second carcass reinforcing structure and the bead cores, so that the edges of the plies of the third carcass reinforcing structure are located at the radially inner side of the bead cores. The first bead wrap ply structure has its turnup portions folded radially outwardly around each bead core, the second carcass reinforcing structure and the third carcass reinforcing structure so that the edges of the plies of the first bead wrap ply structure are located between the radially outer portion of the bead core and the maximum section height of the tire, the first bead wrap ply structure extending axially inward and radially outward from the radially inner portion of the bead core to a radial distance at least one half the radial height of the bead core.
There is still further provided a pneumatic tire having (a) a pair of axially spaced apart bead portions with annular bead cores, each bead core having a radial cross-sectional shape which is substantially round or polygonal; (b) a pair of rubber apex strips of a generally triangular cross-section neighboring the bead cores the apex stripes having a radial height A and extending radially outwardly from the bead cores into the sidewalls of the tire; and (c) a first bead wrap ply structure; (d) at least one set, a second set of carcass reinforcing structures, having a main portion extending between the beads and their edges anchored in the beads. The second carcass reinforcing is folded radially outwardly around each said bead core, so that the two edges of the second carcass reinforcing structure are located between the apexes and their neighboring bead cores. The first bead wrap ply structure has its turnup portions folded radially outwardly around each bead core and the second carcass reinforcing structure so that the edges of the plies of the first bead wrap ply structure are located between the radially outer portion of the bead core and the maximum section height of the tire. The first bead wrap ply structure extends axially inward and radially outward from the radially inner portion of the bead core to a radial distance at least one half the radial height of the bead core.
The invention discloses bead structures having an increased cohesion between the bead core, the carcass plies and the apex through creation of a stiffness gradient between the reinforcement material and the bead core and the rubber of the apex. Furthermore the invention has the bead core act as a pivot, creating thereby a tight interlocking of the carcass plies with the bead core and the apex.
The advantages obtained by the invention are an improved anchoring of the tire structure to the rim. The stress intensive inflection points in carcass bending, located in the upper apex zone in classical prior art constructions, are eliminated trough the concept of a carcass pivoting around the bead core axis. Stress peaks at carcass ply edges are reduced so as to have improved durability of the bead portions. A still further advantage is a reduced occurrence of pulled ply condition in the tire building process.
xe2x80x9cAspect Ratioxe2x80x9d means the ratio of its section height (SH) to its section width (SW).
xe2x80x9cAxialxe2x80x9d and xe2x80x9caxiallyxe2x80x9d means the lines or directions that are parallel to the axis of rotation of the tire.
xe2x80x9cBeadxe2x80x9d means that part of the tire comprising an annular tensile member, the bead core, wrapped by ply cords and shaped, with or without other reinforcement elements such as flippers, chippers, apexes, toe guards and chafers, to fit the design rim. The bead core is usually made of annularly wound steel wire.
xe2x80x9cBelt reinforcing structurexe2x80x9d means at least two annular layers or plies of parallel cords, woven or unwoven, underlying the tread, unanchored to the bead, and having both left and right cord angles.
xe2x80x9cBias plyxe2x80x9d means a tire having bias angled carcass, the angle of the cords being about 35xc2x0 to 65xc2x0 relative to the equatorial plane of the tire. Each adjacent ply has cords equal but oppositely oriented.
xe2x80x9cCarcassxe2x80x9d means the tire structure apart from the belt structure, tread, undertread, and sidewall rubber over the plies, but including the beads.
xe2x80x9cCircumferentialxe2x80x9d means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction.
xe2x80x9cEquatorial Plane (EP)xe2x80x9d means the plane perpendicular to the tire""s axis of rotation and passing through the center of its tread.
xe2x80x9cInnerxe2x80x9d means toward the center of the tire and xe2x80x9couterxe2x80x9d means toward its exterior.
xe2x80x9cPlyxe2x80x9d means a continuous layer of rubber-coated parallel cords. The cords may be of metallic or textile material.
xe2x80x9cRadialxe2x80x9d and xe2x80x9cradiallyxe2x80x9d mean directions radially toward or away from the axis of rotation of the tire.
xe2x80x9cRadial ply tirexe2x80x9d means a belted or circumferentially-restricted pneumatic tire in which the ply cords which extend from bead to bead are laid at cord angles between 65? and 90? with respect to the equatorial plane of the tire.
xe2x80x9cSection Heightxe2x80x9d (SH) means the radial distance from the nominal rim diameter to the outer diameter of the tire at its equatorial plane.
xe2x80x9cSection Widthxe2x80x9d (SW) means the maximum linear distance parallel to the axis of the tire and between the exterior of its sidewalls when and after it has been inflated at normal pressure for 24 hours, but unloaded, excluding elevations of the sidewalls due to labeling, decoration or protective bands.